This invention pertains to the casting of metals in sand molds, and particularly to methods and materials for increasing the lives of the mold patterns which are employed therein.
The introduction of a molten metal into a cavity, or mold, where upon solidification, the resulting casting becomes an object whose shape was determined by the mold, is an old art. Equally as old is sand casting. In this molding process a wood, metal or plastic pattern is fabricated in the shape of the part to be produced. Sand is then compacted around the pattern in such a way that the top portion of the mold and the pattern can be removed, leaving a mold cavity in the shape of the pattern. Molten metal is then poured into the mold cavity.
It is well known that to increase the life of a mold and to make the removal of the casting easier, the surfaces of the mold cavity must be coated with a protective material. In the case of sand castings however it is the pattern which must be coated. Prior art coating compositions however deal primarily with mold coatings rather than pattern coatings.
Coatings for foundry cores and molds are basically mold release agents. They are used to obtain smoother casting surfaces with fewer defects. In its simplest form such a coating is simply a suspension of bentonite, kaolin and other members of the montmorillonite group of clays in water. As in the case of moldings, the use of sandcasting patterns is not without its own problems. The pattern surfaces erode and pit when successive mold cavities are produced using them. When such erosion occurs, molding sands have a greater tendency to adhere to the pattern when it is removed, affecting the mold cavity. Pattern release coatings in accordance with the present invention provide improved release properties and increase the number of molds/application. Accordingly, in spite of available pattern coating compositions, mineral seal oil and mineral seal oil-clay coatings are still the commercial preference.